Apparatus for Spatially and Spectrally Adaptable Dichromatic White Light Source Using Spatial Light Modulator

ABSTRACT

In described examples of an illumination system, the illumination system includes: at least two illumination modules to output different color light beams to an illumination path; and illumination optics corresponding to each of the at least two illumination modules to receive the light beams and to provide illumination to a programmable spatial light modulator. The programmable spatial light modulator receives the illumination and outputs patterned light to projection optics. The projection optics receive the patterned light and output the patterned light as an output beam through a lens. A controller controls the intensity and duration of light output from the at least two illumination modules and controls the pattern of the spatial light modulator. The output beam is a color formed by combining the different color light beams. The output beam is spectrally tunable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. 119(e)to U.S. Provisional Patent Application Ser. No. 62/184,485, filed Jun.25, 2015, entitled “SPATIALLY AND SPECTRALLY ADAPTABLE DICHROMATIC WHITELIGHT SOURCE USING SPATIAL LIGHT MODULATOR,” naming Vikrant R. Bhakta asinventor, which application is hereby incorporated by reference hereinin its entirety.

TECHNICAL FIELD

This relates generally to spectrum adjustable lighting sources, and moreparticularly to patterned, spectrally adjustable light sources utilizinga spatial light modulator.

BACKGROUND

White light is important in many lighting applications such asautomotive headlamps, general lighting, photography, and microscopeillumination. Inconsistency of the observed white color can result inundesirable shifts in appearance. Not all “white” light bulbs give outthe same color white light. Labeling on currently available white bulbsmay indicate “warm” white or “cool” white. The labeling is based on acorrelated color temperature (CCT) rating. CCT indicates the expectedcolor appearance, and it is a simplified representation of the spectralpower distribution (SPD) for a given light source. By industryconvention, a light source with a CCT in the 2700K to 3000K rangeprovides a “warm” white light, while a light source with a CCT in the4000K to 6500K range provides a “cool” white. After the desired whitelight color has been identified, bulbs that are currently available alsohave issues of color consistency between different bulbs having the sameCCT ratings. Also, shifts in the observed color can occur during thelifetime of the light source as components age.

U.S. Patent Publication No. 2015/0252974 to Darwin Hu (“Hu”) disclosescreating white light using two color sources. Hu describes green laserbeams applied to excite a magenta phosphor substrate to create whitelight. However, the white color will still change as the phosphor ages,and as the color output of the blue LEDs changes with age.

SUMMARY

In described examples of an illumination system that outputs a beam oflight from a lens, the system includes at least two illuminationmodules. Each of the illumination modules is arranged to output adifferent color light beam to an illumination path. The system includesillumination optics for the illumination modules that are arranged toreceive the light beams. The illumination optics are arranged to provideillumination to a programmable spatial light modulator. The programmablespatial light modulator is arranged to output patterned light toprojection optics. A controller is configured to control the pattern onthe spatial light modulator and to control the intensity and duration oflight output by the illumination modules. The projection optics arearranged to receive the patterned light and to output the patternedlight through the lens. The spectral color can be adjusted for theentire output beam. Also, the spectral color of the output beam can beadjusted on a pixel basis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a digital micro-mirror (DMD) device in a conventionalprojection system.

FIGS. 2A and 2B illustrate operations of a conventional DMD projectionsystem.

FIGS. 3A and 3B illustrate operations of an alternative conventional DMDprojection system.

FIGS. 4A and 4B are a chart and a graph illustrating the relationship ofdichromatic light sources.

FIGS. 5A and 5B depict an example arrangement including a VSP DMD, and acorresponding pupil diagram.

FIG. 6 illustrates adaptive beam formation in an example arrangement.

FIGS. 7A and 7B illustrate an arrangement including a TRP DMD, and acorresponding pupil diagram.

FIG. 8 illustrates another arrangement including a dichroic mirror.

FIG. 9 is a timing diagram showing an example image frame.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures arenot necessarily drawn to scale.

The term “coupled” may also include connections made with interveningelements, and additional elements and various connections may existbetween any elements that are “coupled.”

An illumination source may be referred to herein as a light source or alamp. For example, a blue illumination source (referred to as a bluelamp or a blue light source) can include one or more blue LEDs, or oneor more blue laser diodes, or a blue incandescent bulb.

Example embodiments provide spatially adaptable and spectrally tunablelight sources using dichromatic illumination. In an example, at leasttwo illumination sources of differing color illuminate a spatial lightmodulator that reflects light, and the reflected light is projected froma lens to form an output beam, such as a white output beam. A controllermodulates the intensity and duration of the illumination sources tospectrally tune the output beam. In additional alternative arrangements,image data can be applied to the spatial light modulator to adapt theoutput beam in shape or in content. While certain examples discussedherein are presented in the context of a headlamp, such as an automotiveheadlamp, the embodiments are not so limited. Example embodiments can beutilized in illumination systems that output light generally. Exampleapplications include: flashlights, spotlights, marine, aviation andvehicle headlamps, industrial lighting, outdoor illumination such asstreet lights, path lights, safety and security lighting, and generallighting fixtures. While white output light is described in certainexamples presented herein, other colors can be output by theembodiments.

FIG. 1 illustrates a conventional arrangement using a digitalmicro-mirror device (DMD) as a spatial light modulator device to projectlight for illumination. DMDs are available from Texas InstrumentsIncorporated in various form factors. In system 10, a single lightsource 14 and illumination optics 15 direct light from the light source14 onto the face of a DMD device 11. The DMD device 11 is formed bymicro-electromechanical system (MEMS) technology that is based in parton semiconductor device processing. An array of micro-mirrors 12 isformed over a semiconductor substrate 17. In an example process, themicro-mirrors are formed of aluminum and are each mounted on a hingedmechanism. The micro-mirrors are attached on a hinge and can be tiltedusing electronic signals applied to electrodes that control a tilt bypivoting the micro-mirrors about an axis. In an example DMD device,thousands or perhaps millions of the micro-mirrors are formed in anarray that forms a VGA, 720p or 1080p resolution imaging device.Individual micro-mirrors 12 are positioned to reflect the light from theillumination optics 15 to a projection lens 18. A beam of light isprojected out of the system 10. The micro-mirrors 12 are individuallyaddressable, and each has an associated memory cell that determines thestate of the micro-mirror during an active illumination period.

The micro-mirrors 12 each have three individual states, which are: afirst “ON” state; a second “OFF” state; and a third “FLAT” state. In theON state, the micro-mirrors 12 in FIG. 1 tilt in a first position awayfrom the FLAT position, due to signals on an electrode that cause thehinges to flex. In system 10, the micro-mirrors 12 are positioned toreflect incoming light from illumination optics 15 outwards to theprojection lens 18 in the ON state. In the OFF state, the micro-mirrors12 tilt in a different position and reflect the light away from theprojection lens 18. In some arrangements, the light is directed to a“light dump” (not shown) or thermal energy collector. By varying thetilt positions using electrical control signals, each of themicro-mirrors 12 can direct reflected light to the projection lens 18.The mirrors can also reflect the light away from the projection lens 18.The FLAT state is the position the micro-mirrors take when no power isapplied to the DMD device. In at least one example, the FLAT position is0 degrees, and a very small pixel (VSP) DMD from Texas InstrumentsIncorporated has an ON state tilt of about +12 degrees and an OFF statetilt of about −12 degrees. Other DMD devices provide different tiltangles, such as +/−10 degrees, or +/−17 degrees.

FIGS. 2A and 2B further illustrate the operation of the micro-mirrors ina conventional projector incorporating a DMD as a spatial lightmodulator. In FIG. 2A, projection system 20 incorporates a singleillustrative micro-mirror 22. In the actual device, the DMD will havethousands or millions of these mirrors 22 arranged in a two dimensionalarray. FIG. 2A illustrates the various positions of the micro-mirrors.In the ON state, the micro-mirror 22 is at a first tilted position ON,such as +12 degrees from the vertical or FLAT position. The illuminationsource 24 is angled at −24 degrees from the zero degree position, whichis aligned with the projection lens 28. When reflecting from the surfaceof a mirror, the angle of incidence (AOI) of the incoming light is equalto the angle of reflection (AOR) of the reflected light; therefore, fora +12 degree tilt, the −24 degree angle for the illumination sourceresults in reflected light at the zero degree position, as shown in FIG.2A. The cone of reflected light labeled ON STATE ENERGY shows thereflected light directed outwards from the VSP micro-mirror 22 at thezero degree position. When the VSP micro-mirror 22 is in the ON state,the light from the illumination source 24 is reflected as the cone oflight labeled ON STATE ENERGY at zero degrees into the projection lens28. The projected light is then output from the system 20. The VSPmicro-mirrors can also be found in a FLAT state position when the DMD isnot powered. When the VSP micro-minors are in the FLAT state, theillumination source is usually not powered in a video projection system.The micro-mirrors in the DMD 22 can also be driven to an OFF state. Inthe OFF state position, the VSP micro-mirror 22 is at a second tiltedposition at an angle of −12 degrees from the FLAT position, and (in theOFF state) the light that strikes the VSP micro-mirror is reflected awayfrom the projection lens 28 and is not output from the system 20, butinstead is output into a light dump 26. Light dump 26 can be a heat sinkthat dissipates heat from the light. When the minor 22 is in the OFFstate, the reflected light is prevented from exiting the system.

In conventional projection systems, the FLAT position of the VSPmicro-minor 22 is usually not operated when light is output from thesystem. All of the DMD micro-mirrors move to the FLAT position whenpower to the DMD device is turned off. The FLAT position is sometimesreferred to as a “parked” or “safe” position for the VSP micro-minor 22.

FIG. 2B illustrates a pupil diagram 29 for the conventional projector,including the pupil positions for the three mirror states (OFF, FLAT,ON) and the pupil position of the light source (LAMP). Also, the pupildiagram 29 shows the approximate position of micro-mirror 22 (FIG. 2A)centered in the ON state pupil. In pupil diagram 29, the illuminationsource for a conventional projector is positioned at pupil positionLAMP. The ON pupil position is adjacent and above the LAMP pupilposition. The FLAT pupil position is adjacent and above the LAMP pupilposition, and the OFF pupil position is adjacent and above the FLATpupil position. As illustrated in the pupil diagram, the positions ofthe pupils are centered on a vertical line due to the VSP micro-mirrorhaving a single acting hinge. This type of VSP DMD is commerciallyavailable and sold by Texas Instruments Incorporated. For example, theTexas Instruments Incorporated device DLP3000 has an array of 608×684micrometer sized mirrors, equating to more than 400,000 micro-minors.

FIGS. 3A and 3B illustrate another DMD technology for projection systemsthat can be included in the embodiments. FIG. 3A shows a “tilt and rollpixel” (TRP) micro-mirror 32 currently available from Texas InstrumentsIncorporated. In TRP technology, the micro-mirrors are formed on acompound hinge (along an axis shown as a dashed line labelled 31)resulting in the micro-mirrors tilting left horizontally from the FLATposition in a first tilt position (which is the ON position) and tiltingdownwards from the FLAT position in a second tilt position (which is theOFF position).

In FIG. 3A light from an illumination source (LAMP 34) is focused on theTRP micro-mirror 32 through a focusing lens set (not shown). When theTRP mirror 32 is in the ON position (ON state), the light beam isreflected from the TRP micro-mirror 32 to the projection lens set 38.When the TRP mirror is in the OFF position (OFF state), the lightreflects from the TRP micro-mirror 32 to a light dump 36. The FLAT stateis not normally utilized for projecting light in a conventionalprojection system; however, if lamp 36 is on while the mirrors are inthe FLAT state, the light reflects from TRP micro-mirror 32 along theaxis labeled FLAT.

FIG. 3B illustrates the pupil diagram 39 for the TRP micro-mirror 32 ofFIG. 3A. The pupil diagram 39 for the TRP DMD is different than thepupil diagram 29 described hereinabove for the VSP DMD 22 shown in FIG.2B. In the TRP pupil diagram 39 of FIG. 3B, the three pupil positions(ON, FLAT, OFF) and the position of the illumination source LAMP areindicated and correspond to the axis positions of the same named itemsin FIG. 3A. Also, the pupil diagram 39 shows the approximate position ofthe TRP micro-mirror 32 centered behind the ON pupil position. Asillustrated, the pupil positions form a right angle due to the compoundhinge of the TRP micro-mirror technology. A commercially available partDLP3114 manufactured by Texas Instruments Incorporated is an example ofa TRP DMD device and has a tilt of +/−17 degrees. As illustrated in theTRP pupil diagram of FIG. 3B, when utilized in a conventional projectorsystem, the TRP DMD is illuminated from the LAMP pupil position. The ONpupil position is adjacent and right of the “lamp” pupil position alonga 34 degree axis. The FLAT pupil position is adjacent and right of theON pupil position along a 34 degree axis, and the OFF pupil position isadjacent and below to the FLAT pupil position along a 34 degree axis.Although the TRP pupil diagram 39 in FIG. 3B is different compared tothe VSP pupil diagram 29 of FIG. 2B, a TRP DMD will enable an aspect ofexample embodiments to function well.

FIGS. 4A and 4B depict charts that illustrate combinations ofdichromatic light to form white light. Table 41 in FIG. 4A correlatesvisible light colors to ranges of wavelengths shown in nanometers.Although colors are continuous throughout the spectrum of visible light,the generally accepted color ranges are indicated in the table of FIG.4A as noted on Wikipedia.org at the uniform resource locator (URL):https://en.wikipedia.org/wiki/Visible_spectrum.

FIG. 4B depicts a graph 43 that indicates complimentary lightwavelengths that are perceived as white light by the human eye when thecolors are combined in the proper proportion. The graph 43 of FIG. 4B isfound in Chapter 20, FIG. 20.2 of the light emitting diode websitelocated at the uniform resource locator (URL):https://www.ecse.rpi.edu/˜schubert/Light-Emitting-Diodes-dot-org. Graph43 of FIG. 4B has light wavelength shown on the Y axis with increasingvalue moving up, and the X axis shows wavelength with increasing valuemoving to the right. The data line labelled 45 indicates thecomplementary wavelengths resulting in the perception of white light asperceived by the human eye. The Y axis begins near the green color rangeat the bottom and moves up to red color at 660 nm. The X axis begins inthe violet color range at 380 nm and extends up to approximately 495 nm(extending through the blue color range). As the data line 45 indicates,numerous colors could be combined to create light that appears white toa human observer. Of special interest in FIG. 4B is the combination ofblue light near 480 nm on the X axis and yellow light near 580 nm on theY axis. A combination of the blue and yellow in the proper proportionwill create a white light as perceived by the human eye.

U.S. Patent Publication No. 2015/0377430, entitled “Hybrid Illuminationfor Headlamp” naming this application's inventor, Vikrant R. Bhakta,(“Bhakta”) as inventor, published Dec. 31, 2015, is co-owned with thisapplication and is hereby incorporated by reference in its entiretyherein. Bhakta describes creating dichromatic white light by combiningyellow and blue light sources. Bhakta discloses a blue laser directed toilluminate a yellow phosphor element, causing it to phosphoresce andemit yellow light; the emitted yellow light is then combined with thedispersed blue laser light beam to create a white light source. Bhaktaalso discloses a dichroic mirror mixing yellow light emitted from thephosphor with additional blue light sourced from a blue LED. The mixedlight creates a “static” white color.

FIGS. 5A and 5B depict an example embodiment utilizing a VSP DMD and acorresponding pupil diagram. In projection system 50, a singleillustrative VSP micro-mirror 52 illustrates the three positions of aVSP micro-mirror in a dichromatic system. The FLAT position occurs whenthe device is unpowered and will be the reference position of 0 degrees.The ON position occurs when the mirror is selected and it tilts to afirst tilted position, such as +12 degrees from the FLAT state. The OFFposition occurs when the mirror is deselected and it tilts to a secondtilted position, such as −12 degrees from the FLAT state. A lens set 58is located on the FLAT state axis of 0 degrees, and this is the exitaxis for white light from the white light system 50. A yellowillumination source 54Y and a blue illumination source 54B are locatedon an axis +/−24 degrees 51 a from the FLAT state position of 0 degrees.Light dumps 56B and 56Y are located on an axis of +/−48 degrees 51 bfrom the FLAT state position of 0 degrees and are essentially heat sinksthat dissipate heat from the light and block light from exiting thesystem. Controller 53 synchronizes the movement of the VSP micro-mirrors52 based on image data supplied electronically by conventional methodsand modulates the illumination sources 54Y, 54B to perform spectraltuning of the white light output.

By outputting yellow and blue light through the system in rapidsequences, and by controlling the time duration for display of theyellow and blue light, the white light at the output can be spectrallytuned by the controller 53. By controlling the respective duty cycles ofthe yellow and blue light, a desired white spectrum light is produced.As the lighting sources age and the respective colors change, the whiteoutput color can be dynamically tuned to return the white spectrum lightto the desired color. Tuning can be achieved by suitable programming ofcontroller 53, so no invasive repair of the system is needed. Thevarious embodiments allow the white output of a system, such as anautomotive headlamp, to be spectrally tuned after manufacture andthroughout the life of the system, without needing to open the system.This can be done simply by programming the controller 53. Dynamicspectral tuning is important, especially when manufacturing headlampsystems for different automotive models, or when shipping headlampsystems to different countries that may impose different standards onthe white color required for vehicle headlamps. Also, easy compensationis achieved for the normal changes in white color that may result as thesystem ages. In applications where a sensor such as a forward lookingcamera or other light sensors are available, the controller 53 can sensechanges in the spectrum of white color that is being output andautomatically compensate the color by spectral tuning of the yellow andblue light sources. Alternatively, the system can be calibrated orrecalibrated on an occasional basis. Also, the addressable pixels in theDMD arrays allow both spatial and spectral tuning, so local portions ofthe output beam can be spectrally tuned using the individual DMD pixelsand controller 53.

In FIG. 5A, yellow light from the yellow lamp 54Y passes through afocusing lens set (not shown) that focuses the yellow light on the VSPmicro-mirrors 52. The VSP micro-mirrors are electrically selected ordeselected individually, based on image data presented electronically tothe DMD by the controller or by another image processing device (notshown). For the electrically deselected mirrors, which tilt to the −12degree or OFF state, the yellow light is reflected from the DMD mirrorsto the lens set 58 to exit the white light system. Electrically selectedmirrors tilt to the +12 degree or ON position, and the yellow lightreflects from the selected DMD mirrors to the yellow light dump 56Y.

For the blue light path in FIG. 5A, blue light from the blue lamp 54Bpasses through a focusing lens set (not shown) that focuses the bluelight on the VSP micro-mirrors 52. In operation, the VSP micro-mirrors52 are electrically selected or deselected based on image data presentedelectronically to the DMD. For the electrically selected mirrors, whichtilt to the +12 degree or ON state, the blue light is reflected from theDMD mirrors to the lens set 58 to exit the white light system.Electrically deselected mirrors tilt to the −12 degree or OFF position,so the blue light is reflected from the DMD mirrors to the blue lightdump 56B. Although the light sources are symmetrically located onopposite sides of the light output axis of 0 degrees as shown in FIG.5A, the blue light is reflected to the output axis when a mirror isselected or in the ON position, while the yellow light is reflected tothe output axis when a mirror is deselected or in the OFF position.

The pupil diagram 59 of FIG. 5B illustrates this relationship. In FIG.5B, five pupil locations (56Y, 54B, 58, 54Y, 56B) illustrate thecombination of the four pupil locations from the yellow lamp, (54Y, 58,54B, 56Y) and the four pupil locations from the blue lamp (54B, 58, 54Y,56B). Locations 58, 54B and 54Y are overlapping for the two diagrams,resulting in the five pupils 56Y, 54B, 58, 54Y, 56B. On the left side ofthe pupil diagram of FIG. 5B, components and states for the yellow lightare noted. The yellow lamp is located at pupil 54Y with the yellow lightoutput on pupil 58 when a VSP micro-mirror is selected for the yellowlamp. A yellow light dump is located at pupil 56Y that receives yellowlight when a VSP micro-mirror is deselected for the yellow lamp. Theposition of the yellow lamp at pupil 54Y, the lens set at pupil 58 andthe yellow light dump at pupil 56B correspond to the same items 54Y, 58,56Y listed in FIG. 5A.

On the right side of the pupil diagram 59 of FIG. 5B, components andstates for the blue light are shown. The blue lamp is located at pupil54B with the blue light output on pupil 58 when a mirror is selected forthe blue lamp. A blue light dump is located at pupil 56B, which receivesblue light when a mirror is deselected for the blue lamp. The positionof the blue lamp at pupil 54B, the lens set at pupil 58 and the bluelight dump at pupil 56B correspond to the same items 54B, 58, 56B listedin FIG. 5A. Because the yellow and blue pupil diagrams have opposingphysical orientations, a mirror that is “selected” for a firstillumination source will be “deselected” for the second illuminationsource.

In operation, the VSP micro-mirrors 52 are modulated between the ON andOFF states at a rapid rate, mixing the blue and yellow light to createthe white light. The amount of blue and yellow light contained in thewhite light beam can be tuned by adjusting a duty cycle (theproportional time spent in the ON and OFF states) for each illuminationcolor. Additional embodiments can be formed by modulating eachillumination source, enhancing the spectral adjustability of the outputlight. The micro-mirrors of the DMD device are individually addressable.In addition to blending the blue and yellow light, patterns can beformed in the beam by further utilizing the DMD as a spatial lightmodulator. Further, because the individual pixels are addressable, thespectral tuning can be extended to a spatial tuning. Regions within theprojected beam can be individually spectrally tuned. In addition toglobal spectral tuning, the arrangements provide local spectral tuning.By rapidly switching the DMD mirror elements between positions toreflect blue and yellow light, the spectral tuning can be combined withspatially addressed regions to form different colored regions within theoutput beam.

The light sources in the example embodiments have different illuminationprofiles. The spectral tuning can compensate for these differences byusing spectral tuning to achieve a uniform output over the entire field.The blue lasers that illuminate the phosphor in FIG. 5A provide aGaussian illumination profile. In contrast, the blue LEDs have a cosineillumination profile. A conventional approach to combining thesenon-uniform illumination beams would include a fly's eye array or lighttunnel to operate as a homogenizer. These known approaches havedisadvantages for a headlamp, because the resulting output will havereduced peak luminance and a uniform beam profile on the road, but anon-uniform profile is actually preferred. In contrast to theconventional approaches, example embodiments provide spatial tuning andspectral tuning, so that a white or other desired spectral output can beachieved. Spectral tuning of the output can be achieved by rapidlyswitching the mirrors in the DMD array between the blue and yellow lightsources, while simultaneously modulating the duty cycle of the lightsources. In additional alternative approaches, individual mirrorelements can be individually adapted to spectrally tune local regions inthe output, such as edge regions, to improve the uniformity of color inthe output beam.

Many recent and recently proposed headlight systems include severalindividual modules for low-beam, high-beam, auxiliary high beam andgeneral illumination. Each of the right and left side headlamps in anautomotive application can incorporate these individual modules. In anexample embodiment, one or more of these individual modules could eachinclude the arrangements described above. In one alternative approach,one of the modules could include the arrangements of the embodiments,while other modules use conventional light sources. In either case,certain conventional modules tend to project a beam that is blue tingedat the outside edges. The spectral and spatially adapted spectral tuningof the embodiments can compensate for the blue edges in the output beamsof these systems by increasing yellow light in these sensitive areas,while the output light is a more balanced white in other areas.

FIG. 6 further illustrates another an adaptive beam embodiment. Inoperation, the mirrors of the DMD (62 a, 62 b) are individuallyaddressable and are rapidly alternated between the blue and yellow lightbeams to form the white light output by a projection system. A depictionof the white light system (while the yellow light is active) is depictedas 60Y. In 60Y: (a) the yellow lamp 64Y is selected, producing yellowlight; and (b) the blue lamp 64B is deselected, producing no light. Inthis example, the majority of mirrors (62 a) reflect the yellow lightbeam to the output. Four mirrors are tilted to not reflect yellow lightto the output, as the uppermost mirror 62 a illustrates. Following thelight beam away from the DMD, the non-lit portion 63 a corresponds tothe mirror 62 a duplicating the pattern depicted by the four non-litmirrors.

The alternate cycle is depicted as 60B, illustrating when the blue lamp64B is selected and producing blue light. The yellow lamp 64Y isdeselected and not producing light. In this cycle, the mirrors shown in62 b have all changed to their respective opposite states, resulting ina majority of the mirrors reflecting blue light to the output. The fournon-lit mirrors, represented as dark mirrors in 62 b, make a pattern inthe light beam where the non-lit space 63 b corresponds to the non-litmirrors in 62 b. As the patterned yellow light and patterned blue arecombined, the output is depicted by the white light output 60W. In thewhite light output 60W, the non-lit section 63 c corresponds to 63 a and63 b. The patterned beam could be totally absent of light as illustratedin 60W. Or, in alternative arrangements, the patterned beam could be adifferent color created by modulating the mirrors in a different dutycycle than the white light mirrors. An example 60F illustrates howexternal row pixels can be modulated to form a yellow light, while thecenter is modulated to form a white light. In an automotive headlampapplication, this pattern can be suitable for foggy conditions. Whilethe example in FIG. 6 shows four mirrors that are tilted differentlyfrom the remaining mirrors in the array, even a single mirror can bespectrally tuned, and the resulting pattern can be spatially adapted onas fine as a single pixel basis. More frequently, several pixels couldbe spatially adapted to form a visible pattern in the output beam.

In an automotive application example, messages useful to a driver can beprojected onto a roadway. For example, if a navigation system iscombined with an automotive headlamp using the arrangements, anavigational cue such as “take next exit” can be projected onto theroadway to assist the driver in following navigational routes. Otherinformation (such as related to traffic, construction, or accidents inupcoming portions of the trip) can be shown on the roadway. For example,these can be shown in blue or in yellow, to further attract the driver'sattention.

The spatial light modulators in the arrangements, along with dichromaticillumination, allows additional adaptive beam shaping. The output beamcan be shaped so as to be “glare free”, so it can be centered brightlyin the middle of a lane being traversed by an automobile. The adaptivebeam shaping can direct light away from oncoming traffic, or away frompedestrians, cyclists or animals that are in the areas adjacent to theroadway. By maintaining bright forward illumination without blindingother observers, the adaptive beam shaping increases driver visibilityand safety. Controller 53 in FIG. 5A can adaptively shape the forwardbeam by appropriately patterning the pixels in the DMD.

FIGS. 7A and 7B illustrate an additional embodiment utilizing a TRP DMD.In the light projection system 70, a single illustrative TRPmicro-mirror 72 illustrates the various positions of the micro-mirrors.In this example, yellow and blue illumination sources form white light.For the yellow light path of FIG. 7A, a first yellow lamp 74Y outputslight focused on the TRP micro-mirror 72 by a focusing lens set (notshown). When the TRP micro-mirror 72, is deselected or in the OFFposition, the yellow light beam is reflected from the TRP micro-mirrorand exits through lens set 78. When the TRP micro-mirror 72 is selectedor is in the ON position, the yellow light is reflected from the TRPmicro-mirror to a light dump 76Y, which is a heat sink to dissipate heatfrom the yellow light. When the DMD is unpowered, the mirrors move tothe FLAT state, and light reflects from the TRP micro-mirror along theaxis 75Y when the yellow lamp is on.

For the blue light path of FIG. 7A, a blue lamp 74B is located about 90degrees counter clockwise from the location of the yellow lamp 74Y, andthe blue light is focused on the TRP micro-mirror 72 array by a focusinglens set (not pictured). When the DMD device is unpowered, the mirror isin the FLAT state, and the blue light reflects from the TRP micro-mirroralong the axis 75B when the blue lamp is illuminated. With the TRPmicro-mirror 72 in the deselected or OFF position, the blue light isreflected to the blue light dump. With the TRP micro-mirror 72 in theselected or ON position, the blue light reflects from the TRPmicro-mirrors and exits through lens set 78.

In operation, the controller 73 alternates the TRP micro-mirrors betweenthe ON state and the OFF state to combine the yellow light and bluelight, and so produces white light. The duty cycles (between the ON andOFF states of the blue and yellow light sources) will determine thecolor of the white light output by the white light system. Also, thecontroller 73 can modulate the intensity of the yellow lamp 74Y and bluelamp 74B to vary the spectral tuning of the white light output.

In this example embodiment, seven pupils are formed when using the TRPDMD in a dichromatic white light system arrangement. The seven pupilsare illustrated in the pupil diagram 79 of FIG. 7B. For convenience, theidentifying numbers of the pupil diagram in FIG. 7B correspond to thepositions in FIG. 7A. The pupil diagram 79 of FIG. 7B illustrates thecombination of the blue pupil diagram and yellow pupil diagram with theON pupil position 78 shared by both yellow and blue light beams. Theapproximate location of the TRP micro-mirrors 72 is indicated behind thecenter-most pupil location 78. In pupil diagram 79, the yellow lamp isshown located in pupil 74Y. When the DMD is unpowered, all the TRPmirrors are in a FLAT or non-tilted position. In the FLAT position, theyellow light 74Y reflects from the TRP micro-mirrors 72 to the yellowFLAT pupil 75Y. When the TRP mirror 72 is deselected or in the OFFstate, the TRP mirror tilts from the FLAT position halfway toward thedirection of the yellow light pupil 74Y. The yellow light reflects fromthe TRP micro-mirrors in the OFF state and exits the system throughpupil 78. With the TRP micro-mirrors selected in the ON state, themirror tilts from the FLAT position halfway toward the direction of theblue lamp pupil 74B. The yellow light reflects from the TRPmicro-mirrors 72 to the yellow TRP-ON pupil 76Y.

In FIG. 7B, the blue lamp is shown in pupil 74B. When the DMD isunpowered, the TRP micro-mirrors are in a FLAT or non-tilted position.In the FLAT state, the blue light 74Y reflects from the TRP mirror tothe blue light FLAT pupil 75B. As mentioned hereinabove, when a TRPmicro-mirror is selected or in the ON state, the TRP micro-mirror tiltsfrom the FLAT position halfway toward the direction of the blue lightpupil 74B. In the ON state, the blue light reflects from the TRPmicro-mirrors and exits the system through pupil 78. With a TRPmicro-mirror deselected or in the OFF state, the mirror tilts from aFLAT position halfway toward the direction of the blue lamp pupil 74Y.In the OFF state, the blue light reflects from the TRP micro-mirror 72to the blue TRP-OFF pupil 76B. The TRP micro-mirrors of the DMD TRPdevice are individually selected or deselected. In addition to blendingthe blue light and yellow, patterns can be formed in the output beam byutilizing the TRP DMD as a spatial light modulator. Patterns arepresented to the controller 73 in the form of electronic image data. Forexample, the patterns illustrated in FIGS. 6A and 6B can be formed withthe TRP DMD shown in FIG. 7A.

FIG. 8 depicts another alternative embodiment utilizing a dichroicmirror. In system 80, a blue laser 81 excites a yellow phosphor 85 toproduce yellow light. Blue light from LEDs 86 is combined with theyellow light to form a white light beam. In system 80, a set of one ormore blue laser diodes 81 outputs blue laser light beams directed to adichroic mirror 83. The dichroic mirror 83 allows yellow light to passand reflects blue light. The dichroic mirror 83 is positioned to reflectthe blue laser light through a focusing lens set 84 and onto the surfaceof yellow phosphor substrate 85. The yellow phosphor substrate 85phosphoresces when struck by the blue laser light beam and emits yellowlight. The yellow light 850 travels through the lens set 84 and towardsthe dichroic mirror 83. The dichroic mirror 83 is configured to allowyellow light to pass through, and the yellow light beam 850 proceedstoward a focusing lens set 88. A blue light source 86, such as a blueLED, outputs blue light 860 that passes through lens set 87 to thedichroic mirror 83. The dichroic mirror 83 reflects the blue light. Theblue light 860 reflects from the dichroic mirror and is combined withthe yellow light 850 to produce a white light 803 a. The white lightbeam 803 b passes through the focusing lens set 88 and is then focusedon a spatial light modulator, which is a DMD 810 in this example. Thedesired portion of the white light beam 803 b is reflected by the DMD810, resulting in a patterned white light beam 803 p. A pattern isformed in the white light beam 803 p, determined by image dataelectronically presented to the DMD 810 by controller 830. The patternedlight beam 803 p then passes through the projection lens set 880 andexits the dichromatic light system.

In system 80, controller 830 performs functions such as: (a) modulatingthe amount of blue light outputted by the blue lamp 86; (b) modulatingthe power of the blue laser source 81 to modulate the amount of yellowlight emitted by phosphor 85; and (c) presenting electronic image datato the DMD 810 to implement a desired pattern, if any, within thethousands of individually selectable micro-mirrors of the DMD, resultingin a patterned, spectrally adjustable and/or spatially adaptable whitelight beam.

In example embodiments, controller 830 can be implemented as anintegrated circuit, which can be a dedicated integrated circuit. Inalternative embodiments, the functions performed by the controller 830can be provided by a programmable integrated circuit, such as a digitalsignal processor (DSP), microcontroller unit (MCU), or centralprocessing unit (CPU) programmed with corresponding softwareinstructions. In other examples, the functions of controller 830 can beprovided by modifying the existing operations of an existing integratedcircuit for use with spatial light modulators. The modifications can addinstructions to control the spectral color emitted by the dichromaticlight sources. User defined integrated circuits (such as fieldprogrammable gate arrays (FPGAs), complex logic programmable devices(CLPDs) and ASICs) can implement controller 830.

In additional embodiments, the yellow light beam 850 and the blue lightbeam 860 can be transported in free air as shown hereinabove, or in analternative transport medium for light, such as a light tunnel,waveguide or fiber optic transport.

The arrangements can operate with digital color correction to correctthe color at the output by controlling the DMD mirrors and controllingthe light source modulation. The color correction can be donecontinuously in example systems including a color sensor. In otherexamples, the color correction can be done periodically by adapting thelight source modulation in a calibration operation.

FIG. 9 is a timing diagram 90. In FIG. 9, a single frame is shown (therewill be many frames projected per second from the DMD in operation)where color correction is performed. In the single frame 901, bothyellow and blue light sources are illuminated and reflected in the firstportion of the frame, Subframe 1, labeled 903. In a second portion ofthe frame 901, Subframe 2, labeled 905, only the blue LED source isilluminated and reflected, so that blue light is projected at theoutput. In a third portion of the frame 901, Subframe 3, labeled 907,only the laser-phosphor illumination is illuminated and reflected, sothe projected light is yellow for Subframe 3. A pixel level colorcorrection mask can be applied either on a blue subframe or on a yellowsubframe to modify relative contributions of yellow and blue light inareas projected on the road. In this manner, the output color can betuned, both spectrally and spatially.

FIG. 9 shows the time weight of the various subframes, so: Subframe 1 iswhite due to the combination of the two colors; Subframe 2 is blue inthis example frame; and Subframe 3 is yellow in this example frame. Thesubframes can be modulated using a duty cycle approach. The output coloris spectrally tuned by the percentage weights (such as 13.3% white,43.3% blue and 43.3% yellow in this example) for the single frame'stotal time. The light output from yellow and blue light sources can alsobe varied by changing the input power to the blue LEDs and lasers.Because the human visual system integrates the light at the output, thecolor seen by a human observer is the combination of the subframecolors.

Example embodiments provide a low cost illumination system that isspectrally tunable and also spatially tunable to perform beam shaping ofthe output beam. Arrangements are low in cost and can be adaptivelyspectrally tuned after manufacture, to adjust the light color throughoutthe life of the system. In some embodiments, continuous spectral tuningcan be provided.

Accordingly, in described examples, an illumination system is arrangedto project an output beam of light forward from a lens. The illuminationsystem further includes: at least two illumination modules, eachconfigured to output a light beam to an illumination path, theillumination modules arranged to output different color light beams; andillumination optics corresponding to each of the illumination modules,arranged to receive the different color light beams and arranged toprovide illumination to a programmable spatial light modulator. Theprogrammable spatial light modulator is arranged to receive theillumination and is arranged to output illumination as patterned lightto projection optics. The projection optics are arranged for receivingthe patterned light and further arranged to output the patterned lightthrough the lens. A controller coupled to the illumination modules andto the spatial light modulator is arranged to control the intensity andduration of the light output by the illumination modules and to controla pattern of the spatial light modulator. The output beam is a colorformed by combining the different color light beams, and the output beamis spectrally tunable.

In a further example, the spatial light modulator includes a digitalmicro-mirror device. In some examples, the digital micro-mirror devicehas tilt positions that are at +/−12 degrees with respect to anunpowered position. In another example, the digital micro-mirror devicehas tilt positions that are at +/−17 degrees with respect to anunpowered position.

In at least one example, the first illumination module of theillumination modules is arranged to produce a light beam color using aphosphor. In another example, a second illumination module of theillumination modules is arranged to produce a light beam color withoutusing a phosphor. In yet another example, the combined colors of thelight beams output by the two illumination modules produce a white lightbeam. In an alternative example, a first illumination module of theillumination modules is arranged to output a yellow light beam and asecond illumination module of the illumination modules is arranged tooutput a blue light beam. In still a further alternative example, thecolor of the output beam is spectrally tunable.

In yet another example, the illumination system further includes adichroic mirror positioned to direct the light beams of the illuminationmodules onto the spatial light modulator. In still another example, thespatial light modulator is arranged to adaptively change a pattern ofthe output beam responsive to the controller. In a further example, theoutput beam is spectrally tunable over an entire image. In anotherexample, the output beam is spectrally tunable on a pixel basis.

An example automotive headlamp includes: a first illumination sourcearranged to output a first color light; a second illumination sourcearranged to output a second color light different from the first colorlight; a digital micro-mirror device directed to receive the first colorlight and to receive the second color light; projection optics arrangedto receive light reflected from the spatial light modulator and arrangedto output a beam that has a color that is a combination of the first andsecond colors; and a controller arranged to control the intensity andduration of the first illumination source and the second illuminationsource and arranged to control a pattern on the digital micro-mirrordevice; wherein the controller is arranged to spectrally tune the colorof the output beam.

In another example, the first illumination source in the automotiveheadlamp further includes a phosphor arranged to emit light whenilluminated; and an illumination source arranged to illuminate thephosphor. In yet another example, the automotive headlamp includes ayellow phosphor and the first color light is yellow light. In anotherexample, the automotive headlamp includes the second illumination sourcearranged to emit light without a phosphor. In a further example, thesecond illumination source is arranged to emit the second color lightthat is blue. In an additional example, in the automotive headlamp, theprojection optics are arranged to output a beam of white light that is acombination of the first color light and the second color light.

Another example illumination system includes: a digital micro-mirrordevice arranged to reflect illumination light as a patterned light beam;projection optics positioned to receive the patterned light beam andarranged to project an output light beam; a first illumination sourcearranged to output light of a first color and further including laserdiodes positioned to output light and including a phosphor positioned toreceive the output light after it is reflected from a first surface of adichroic mirror. The phosphor is arranged to output the first colorlight in response to the output light. A second illumination source isarranged to output light of a second color different from the firstcolor and is positioned to illuminate a second surface of the dichroicmirror. Illumination optics are arranged to receive reflected light ofthe second color from the second surface of the dichroic mirror andfurther arranged to receive the first color light from the phosphortransmitted through the dichroic mirror. The illumination optics arepositioned to transmit the received light of the first color and thesecond color to a surface of the digital micro-mirror device. Acontroller is arranged to control intensity and duration of the lightfrom the first illumination source and to control the intensity andduration of the light from the second illumination source and furtherarranged to control the pattern on the digital micro-mirror device. Thelight beam output from the illumination system is arranged to be avisibly white light that is a combination of the first color and thesecond color. In another example, the controller is arranged tospectrally tune the white light.

Modifications are possible in the described embodiments, and otherembodiments are possible that are within the scope of the claims.

What is claimed is:
 1. An illumination system configured to project anoutput beam of light forward from a lens, the illumination systemcomprising: at least two illumination modules, each configured to outputa light beam to an illumination path, the at least two illuminationmodules configured to output different color light beams; illuminationoptics corresponding to each of the at least two illumination modules,configured to receive the different color light beams and configured toprovide illumination to a programmable spatial light modulator; thespatial light modulator configured to receive the illumination andconfigured to output patterned light to projection optics; theprojection optics configured to receive the patterned light andconfigured to output the patterned light as an output beam through thelens; and a controller coupled to the at least two illumination modulesand to the spatial light modulator, configured to control the intensityand duration of light output from the at least two illumination modulesand configured to control a pattern of the spatial light modulator;wherein the output beam is a color formed by combining the differentcolor light beams, and the output beam is spectrally tunable.
 2. Theillumination system of claim 1, wherein the spatial light modulatorfurther includes a digital micro-mirror device.
 3. The illuminationsystem of claim 2, wherein the digital micro-mirror device has tiltpositions at +/−12 degrees with respect to an unpowered position.
 4. Theillumination system of claim 2, wherein the digital micro-mirror devicehas tilt positions at +/−17 degrees with respect to an unpoweredposition.
 5. The illumination system of claim 1, wherein a firstillumination module of the at least two illumination modules isconfigured to produce a light beam color using a phosphor.
 6. Theillumination system of claim 5, wherein a second illumination module ofthe at least two illumination modules is configured to produce a lightbeam color without using a phosphor.
 7. The illumination system of claim1, wherein the output beam is a white light beam.
 8. The illuminationsystem of claim 1, wherein a first illumination module of the at leasttwo illumination modules is configured to produce a yellow light beam,and wherein a second illumination module of the at least twoillumination modules is configured to produce a blue light beam.
 9. Theillumination system of claim 1, wherein the color of the output beam isspectrally tunable over an entire image.
 10. The illumination system ofclaim 1, wherein the system further comprises a dichroic mirrorpositioned to direct the light beams of the at least two illuminationmodules onto the spatial light modulator.
 11. The illumination system ofclaim 1, wherein the spatial light modulator is configured to adaptivelychange a pattern of the output beam responsive to the controller. 12.The illumination system of claim 11, wherein the color of the outputbeam is spectrally tunable on a pixel basis.
 13. An automotive headlamp,comprising: a first illumination source configured to output a firstcolor light; a second illumination source configured to output a secondcolor light different from the first color light; a digital micro-mirrordevice configured to receive the first color light and the second colorlight and to reflect the first color light and the second color light; aprojection optics configured to receive reflected light from the digitalmicro-mirror device and configured to output a beam from the automotiveheadlamp that has a color that is a combination of the first and secondcolors; and a controller configured to control intensity and duration ofthe first illumination source and the second illumination source and tocontrol a pattern on the digital micro-mirror device; wherein thecontroller is configured to spectrally tune the color of the outputbeam.
 14. The automotive headlamp of claim 13, wherein the firstillumination source further includes: a phosphor configured to emitlight when illuminated; and an illumination source configured toilluminate the phosphor.
 15. The automotive headlamp of claim 14,wherein the phosphor is yellow, and the first color light is yellowlight.
 16. The automotive headlamp of claim 13, wherein the secondillumination source is configured to emit light without a phosphor. 17.The automotive headlamp of claim 16, wherein the second illuminationsource emits blue light.
 18. The automotive headlamp of claim 13,wherein the projection optics is configured to output a beam of whitelight that is a combination of the first color light and the secondcolor light.
 19. An illumination system, comprising: a digitalmicro-mirror device configured to reflect illumination light as apatterned light beam; projection optics positioned to receive thepatterned light beam and to project an output light beam; a firstillumination source configured to output light of a first color andfurther comprising laser diodes positioned to output light and aphosphor positioned to receive the output light after it is reflectedfrom a first surface of a dichroic mirror, the phosphor configured toemit the first color light in response to the output light; a secondillumination source configured to output light of a second colordifferent from the first color and positioned to illuminate a secondsurface of the dichroic mirror; illumination optics configured toreceive reflected light of the second color from the second surface ofthe dichroic mirror and further configured to receive the first colorlight from the phosphor transmitted through the dichroic mirror, andconfigured to transmit the received light of the first color and thesecond color to a surface of the digital micro-mirror device; and acontroller configured to control intensity and duration of the lightfrom the first illumination source and to control intensity and durationof the light from the second illumination source, and further configuredto control the pattern on the digital micro-mirror device; wherein theoutput light beam is a visibly white color that is a combination of thefirst color and the second color.
 20. The illumination system of claim19, wherein the controller is configured to spectrally tune the whitelight over a portion of an entire beam.